The present invention relates to x-ray machines, and, in particular, to x-ray machines having film trays that mechanically center the film cassette laterally upon the x-ray table.
It is well known that many x-ray machines have examination tables with film cassette (bucky) trays therein that mechanically center the film cassettes of varying sizes on a longitudinal center line of the table. The bucky tray can move longitudinally on the table, but not laterally except for the purpose of inserting and removing film cassettes. Another feature is a collimating means located in the x-ray head. By use of the collimating means, the area of exposure may be adjusted to minimize unnecessary exposure to the patient where a reticle is projected onto the table. The size of the projected reticle is controlled by a diaphragm therein. The x-ray source is typically positioned on the longitudinal center line of the x-ray table.
If one desired to take multiple exposures on one sheet of film, each exposure was always centered on the film because of the bucky tray centering device. Depending upon the film size and the collimated area, 2 or 3 exposures could be placed on One sheet of film. It is clear from this standard practice that a significant amount of film area was wasted.
Prior devices, for example, to maximize film usage are as follows: U.S. Pat. No. 1,219,965 discloses a partially enclosed tray having a rectangular opening therein. The film is moved within the tray to expose selected areas. This device has a fixed opening size therein. The opening is fixed within the tray and limited to a certain film size. U.S. Pat. No. 2,545,899 discloses a partially enclosed film tray having movable openings to produce multiple exposures. The size of the openings are fixed as well as the distance from the center thus only a particular film size would produce optimum results. U.S. Pat. No. 3,955,656 discloses a film tray moveable under an aperture on an x-ray table. The tray is marked for a fixed size of film cassette and is able to produce multiple exposures by adjusting the cassette in the tray according to the guide lines thereon. These patents fail to address the problem of the present invention wherein film cassettes of various sizes are used in a buck tray having a fixed mechanically centering device therein.
The need exists for an apparatus and method for being able to take multiple exposures of a size to be determined by the medical procedure and to optimize this size to the size of the film being used in a mechanically operated x-ray machine.